Myeloablative regimens are the backbone of hematopoietic stem cell transplantation (HSCT) and are associated with prolonged periods of cachexia/anorexia, nausea/vomiting, mucositis, and compromised gut integrity (CGI). The toxicities associated with HSCT often lead to prolonged periods of poor oral intake and may result in overt malnutrition. CGI decreases oral tolerance to foods, reduces Quality of Life (QOL) and functional status, delays the transition from the hospital to home setting, and increases the risk of the development of gut-derived infections. Probiotics are nutritional supplements that contain a defined amount of viable microorganisms and upon administration confer a benefit to the host. Clinical trials in adults receiving organ transplants have found probiotics decrease the incidence of infection, the duration of antibiotic use, the incidence of multiorgan failure and systemic inflammation. Children and adolescents undergoing HSCT, experience similar clinical challenges suggesting probiotics may have a therapeutic value in the setting of HSCT. This study is to evaluate the safety and feasibility of administering probiotics to children and adolescents undergoing HSCT.